Metro News & Reviews

New video: time-lapse of digging of first Regional Connector tunnel

New footage from the Regional Connector project in downtown Los Angeles shows how the tunnel boring machine has completed building the first of two twin tunnels under the city center. Work on the mile-long tunnel started in February of this year in Little Tokyo and was completed last week in the Financial District.

The Regional Connector will link three existing light-rail lines (the Gold, Expo, and Blue Lines) and add three new underground stations in downtown Los Angeles between Little Tokyo and 7th/Metro stations. When done, the project will create two light rail lines — one will run between East Los Angeles and Santa Monica and the other between Azusa and Long Beach. The two lines will share five downtown L.A. stations and make travel to and through DTLA faster with fewer transfers.

Angeli, as the TBM is named, began her journey at the future Little Tokyo/Arts District Station and bore 5,820 feet to the retrieval point at 4th and Flower streets. Along the way she traveled through the future Historic Broadway Station (at 2nd and Broadway) and made an appearance at the future Grand Av Arts/Bunker Hill Station (at 2nd and Hope) earlier in the summer.

The tunnel runs primarily down 2nd Street, which means the TBM successfully dug beneath the existing Red Line subway — at its deepest point, the tunnel runs 100 feet below ground. Soil conditions were favorable as most of the tunneling occurred within the Fernando Formation, the bedrock found across much of the L.A. Basin. In total, approximately 65,000 cubic yards of soil were excavated.

With the first tunnel complete, crews will remove the TBM’s cutterhead and shield segments this weekend and send the machine’s trailing gear back through the finished tunnel. Angeli will undergo maintenance and be rebuilt in Little Tokyo where she will start work on the second tunnel at the end of the summer. The second tunnel is expected to be complete by early next year.

The remainder of the 1.9-mile underground alignment—from 4th Street to just south of 6th Street — will be constructed using “cut and cover” tunneling down Flower Street. As the name suggests, crews will dig a large trench which is then covered with concrete decking to maintain vehicle traffic on the surface. With the deck in place, construction work can continue below ground. Flower Street decking is finished up to 5th Street and will continue south later this summer.